AU2021202108A1 - A process for preparing a paraffin product - Google Patents

Abstract

A PROCESS FOR PREPARING A PARAFFIN PRODUCT Abstract The invention relates to a process for preparing a paraffin product from a carbonaceous feedstock. The method comprises the steps of obtaining a gaseous mixture of carbon monoxide and hydrogen from a carbonaceous feedstock, performing a Fischer-Tropsch reaction and subjecting at least part of an off gas obtained from the Fischer-Tropsch reaction to fermentation.

Description

A PROCESS FOR PREPARING A PARAFFIN PRODUCT

Cross Reference The present application is a divisional application of Australian Patent Application No. 2017236342, the content of which is incorporated herein by reference in its entirety. Australian Patent Application No. 2017236342 is the Australian National Phase Entry for International Patent Application No. PCT/EP2017/056616, which claims priority to EP 16161563.8, filed on 22 March 2016, the content of which is also incorporated herein by reference in its entirety.

Field of the invention The present invention relates to a process for preparing a paraffin product from a carbonaceous feedstock.

Background to the invention The Fischer-Tropsch process can be used for the conversion of hydrocarbonaceous feed stocks into normally liquid and/or solid hydrocarbons (i.e. measured at 0° C, 1 bar). The feed stock (e.g. natural gas, associated gas, coal-bed methane, residual oil fractions, biomass and/or coal) is converted in a first step into a mixture of hydrogen and carbon monoxide. This mixture is often referred to as synthesis gas or syngas. The synthesis gas is fed into a reactor where it is converted over a suitable catalyst at elevated temperature and pressure into paraffinic compounds ranging from methane to high molecular weight molecules comprising up to 200 carbon atoms, or, under particular circumstances, even more.

The hydrocarbon products manufactured in the Fischer-Tropsch process are processed into different fractions, for example a liquid hydrocarbon stream comprising mainly CS+ hydrocarbons, and a gaseous hydrocarbon stream which comprises methane, carbon dioxide, unconverted carbon monoxide, unconverted hydrogen, and lower hydrocarbons. The gaseous hydrocarbon stream may also comprise nitrogen, argon and traces of olefins and oxygenates

The gaseous hydrocarbon stream is often referred to as Fischer-Tropsch off-gas. Fischer Tropsch off-gas can be recycled to the syngas manufacturing or to the Fischer-

Tropsch reactor. Sometimes lower hydrocarbons are removed

before the off-gas is recycled. Lower hydrocarbons may be

removed by decreasing the temperature of the off-gas and

then applying a vapour-liquid separation. However, when the

off-gas is recycled to the syngas manufacturing or to the

Fischer-Tropsch reactor, the components in the off-gas

which do not take part in the Fischer-Tropsch reaction,

such as carbon dioxide, nitrogen and methane, occupy

reactor space. The components which do not take part in the

Fischer-Tropsch reaction are also referred to as "inerts".

The level of inerts in the Fischer-Tropsch reactor

increases with increasing Fischer-Tropsch off-gas

recycling. The pace of the build-up of inerts can be

reduced by treating the off-gas before it is recycled. One

possibility is to recycle part of the Fischer-Tropsch off

gas to one or more Fischer-Tropsch reactors while another

part of the off-gas is used as fuel. A downside of this is

that only a part of the hydrocarbonaceous feed stock is

converted to the desired C5+ hydrocarbons. When the off-gas

is passed through a pressure swing adsorption unit (PSA),

it is normally possible to remove carbon dioxide and water

from the off-gas.

It is often possible to recover a hydrogen stream from

the off-gas by means of a PSA unit; the hydrogen stream can

be recycled to the Fischer-Tropsch reactor. Nevertheless,

some common commercial PSA units do not or do not

completely remove nitrogen from the off-gas and result a

hydrogen stream that contains nitrogen. Additionally,

common commercial PSA units are often not designed to

recover a carbon monoxide stream. Therefore, it is common

to recycle only a relatively small part of the off-gas.

There remains a need for improving the processing of

off-gas from Fischer-Tropsch reactions.

Summary of the invention

It has now been found that off gas from a Fischer

Tropsch reaction can be used in fermentation processes to

obtain alcohols.

In an aspect the invention resides in a process for

preparing a paraffin product from a carbonaceous feedstock

comprising the following steps:

(a) Treatment of the carbonaceous feedstock to obtain a

gas mixture comprising hydrogen and carbon monoxide;

(b) Performing at least once, a Fischer-Tropsch

reaction using the mixture as obtained in step (a) and

recovering a paraffin product and an off-gas comprising

hydrocarbons, carbon dioxide, carbon monoxide, water and

hydrogen and optionally, nitrogen, argon and traces of

olefins and oxygenates, from the Fischer-Tropsch reaction;

and

(c) Subjecting at least a part of the off-gas from the

Fischer-Tropsch reaction, optionally after removing

hydrocarbons, to anaerobic fermentation to obtain a

fermentation product comprising alcohol.

Brief description of the drawings

Figure 1 shows a non-limiting example of the present

invention.

Detailed description of the invention

In the present disclosure with fermentation is meant

the conversion of at least CO into alcohol by microbes.

These microbes are capable of growing on CO-containing

gases. Said microbes may or may not require sugar. Such a

process is disclosed in US2011/0138684 which discloses a method of processing synthesis gas obtained from biomass by subjecting it to fermentation. It does not disclose fermentation based on off gas from a chemical reaction.

Off gasses have a different composition than synthesis

gas. Off gasses have a lower carbon monoxide and hydrogen

content and comprise other additional ingredients of which

some may have, by presence or amount, a detrimental effect

on the fermentation process. The off gas used in the

present invention comprises hydrocarbons, carbon dioxide,

carbon monoxide, water and hydrogen and optionally,

nitrogen, argon and traces of olefins and oxygenates. The

inventors found that an off gas comprising these

ingredients can be processed with fermentation.

Said fermentation may be conducted in a bioreactor. The

term bioreactor is meant to include devices such as a

bubble column, trickle bed reactor (tbr), gas lift

fermenter, continuous stirred tank reactor (cstr),

immobilized cell reactor (icr), membrane reactor including

hollow fibre membrane bioreactor (hfmbr), or a static

mixer. Processes for the production of ethanol and other

alcohols from gaseous substrates are known. Fermentation

processes include those described for example in

W02007/117157, W02008/115080, US 6,340,581, US 6,136,577,

US 5,593,886, US 5,807,722 and US 5,821,111.

In the present disclosure, with "a" and "an" is meant "at least one" unless indicated otherwise.

In step (a) of the process the carbonaceous feedstock

is treated to obtain a gas mixture comprising hydrogen and

carbon monoxide.

The treatment of the carbonaceous feedstock in step (a)

is such that a gas mixture comprising carbon monoxide and hydrogen is obtained. This gas mixture is often referred to as syngas. Several methods are known for generating syngas from a carbonaceous feedstock. In an aspect of the invention the production of syngas from hydrocarbonaceous feedstock is effected by any one of gasification, partial oxidation, auto- thermal reforming, steam reforming, or any combination thereof.

In an aspect of the invention the gas mixture is

obtained in step (a) by steam reforming and/or from the

partial oxidation of natural gas. In an aspect of the

invention partial oxidation is used form the production of

synthesis gas from natural gas.

In an aspect the gas mixture is obtained by partial

combustion of coal.

In a Fischer-Tropsch reaction a carbon monoxide and

hydrogen containing gas mixture is contacted with a

Fischer-catalyst in a reactor. Hence, in an aspect of the

invention a step of contacting the gaseous mixture with a

Fischer-Tropsch catalyst is included.

The Fischer-Tropsch reaction may be conducted in a

fixed bed reactor, especially multi-tubular fixed bed

reactor, fluidized bed reactor, such as entrained fluidized

bed reactors and fixed fluidized bed reactor, and slurry

bed reactor such as three-phase slurry bubble columns and

ebulated bed reactors.

In case a fixed bed reactor is used, the Fischer

Tropsch reaction is preferably carried out at a temperature

in the range from 125 to 400 0C, more preferably 175 to 300

°C, most preferably 200 to 260 0C. The pressure preferably

ranges from 5 to 150 bar, more preferably from 20 to 80

bar. The gaseous hourly space velocity may vary within wide ranges and is typically in the range from 500 to 10000

Nl/l/h, preferably in the range from 1500 to 4000 Nl/l/h.

The hydrogen to CO ratio of the feed as it is fed to the

catalyst bed generally is in the range of 0.5:1 to 2:1. In

such a case a cobalt based catalyst is preferred.

Said off gas is used as a gaseous feedstock for

fermentation. In an aspect of the invention at least part

of the residual hydrocarbons present in the off gas are

removed prior to subjecting the off gas to fermentation.

Part of the residual hydrocarbons may be largely removed by

subjecting the off gas to scrubbing in a scrubber or by

cooling the off gas, for example to a temperature of 400C

or less. In the scrubber the off gas is, optionally after

cooling, contacted with a wash fluid comprising C5-C20

hydrocarbons. See for an example W02014/013087.

US2011306682 discloses another method of removing

hydrocarbons from Fischer-Tropsch off gas. The method of

US2011306682 includes absorbing light hydrocarbon compounds

and a carbon dioxide gas from the off gas using an

absorption solvent including liquid hydrocarbon compounds

and a carbon dioxide gas absorbent, separating the

absorption solvent which has absorbed the light hydrocarbon

compounds and the carbon dioxide gas into the liquid

hydrocarbon compounds and the carbon dioxide gas absorbent.

In an aspect the off gas obtained from the Fischer

Tropsch reaction comprises methane, carbon dioxide, carbon

monoxide and hydrogen and optionally water, nitrogen, argon

and traces of olefins and oxygenates. Preferably, the

carbon monoxide content of the off gas is at least 5 vol%

based on the total volume of the off gas. Preferably, the

CO content is at the most 80 vol%. In an aspect of the invention the hydrogen content of the off gas is at least 5 vol%.

In an aspect of the invention the Fischer-Tropsch

reaction is conducted at elevated pressure and the process

comprises a further step prior to step (c) wherein the off

gas pressure is lowered to a pressure of less than 10 bar,

prior to subjecting said off gas to fermentation. This

provides for a good fermentation in which at least 50% of

the carbon monoxide is converted into alcohol. In an aspect

of the invention the pressure is maintained within a range

of 1 to 10 bar. In an aspect of the invention the off gas

is subjected to a pretreatment step prior to step (c) in

which the carbon monoxide level is adjusted such that the

CO level is at least 20 vol%. A gas having a CO level of at

least 20 vol% is suitable for use as a gaseous feedstock

for fermentation.

The carbon monoxide and/or hydrogen level in the

Fischer-Tropsch off gas may vary over time and may drop to

levels below the level required to maintain the

fermentation activity in the bioreactor. A drop in carbon

monoxide level may for example be caused by a change in the

composition of the carbonaceous feedstock or operational

aspects such as a runaway of a Fischer-Tropsch reactor. In

such cases carbon monoxide may be added to the off gas

stream. In an aspect of the invention step (c) is performed

in case the carbon monoxide level in the Fischer-Tropsch

off gas drops to below a certain level, preferably in case

the carbon monoxide level in the off gas is less than 20

vol%.

In fermentation processes the gaseous feedstock is

important for providing appropriate conditions for the microbes to grow, to be maintained and to produce alcohol.

The inventors have found that off gas obtained from a

Fischer-Tropsch reaction is of sufficient quality to be

used as a gaseous feedstock for fermentation. Preferably,

the hydrogen : carbon monoxide ratio is at least 0.01. In a

further aspect of the invention the hydrogen carbon

monoxide ratio is at least 0.2 and in yet another aspect

the ratio is at least 0.4. The off gas obtained from a

Fischer-Tropsch reaction performed at industrial scale

contains methane, carbon dioxide, carbon monoxide and

hydrogen and optionally nitrogen, argon and traces of

olefins and oxygenates. The levels of the different

ingredients may depend on the hydrocarbonaceous feedstock

used.

Hence, the method of the invention allows for the

conversion of CO in off-gas into useful fermentation

products such as ethanol. This improves the efficiency of

the conversion of carbonaceous feedstock into useful

products. Further by converting CO into useful products

carbon dioxide emission is reduced.

In an aspect the off gas is obtained from a second or

further Fischer-Tropsch reaction. This may be achieved by

connecting two or more Fischer-Tropsch reactors in series.

In an aspect of the invention, the off gas of the

fermentation process may be subjected to treatment step (a)

of the process of the invention. This allows for an

improvement in the efficiency of the process.

Depending on the stage of the process, i.e. growing

microbes or producing alcohol, the content of the gaseous

feedstock may be adapted. For example, prior to the start

of the fermentation, microbes need to be multiplied / grown. At such a stage it may be beneficial to provide a gaseous feedstock having a high CO content. This may be achieved by providing off gas obtained from a first

Fischer-Tropsch reaction, from syngas obtained from partial

oxidation or a mixture thereof. It is to be noted that a

too high a concentration of CO may lead to inhibition of

fermentation or growth of the microbes.

In an aspect of the invention step (c) is performed in

at least two bioreactors. In case of two or more reactors

these reactors are preferably provided with off gas in

parallel. This has as an advantage that off gas may still

be processed by one reactor while the other reactor is

taken offline. This may happen in case one bioreactor has

to be provided with a new culture of microorganisms.

In an aspect of the invention the fermentation is

affected by at least one member of the Carboxydotrophic

bacteria such as Clostridium autoethanogenum.

In an aspect hydrogen is removed from the off gas prior

to fermentation by means of pressure swing adsorption or

after fermentation from a second off gas obtained in step

(c). It is preferred that hydrogen is removed after

fermentation. Hydrogen may be removed from the gas obtained

from the fermentation process by use of pressure swing

adsorption.

In an aspect of the invention a part of the gas mixture

obtained in step (a) is subjected to anaerobic fermentation

to obtain a fermentation product comprising alcohol. This

may be useful in case the off gas generated in step (b)

cannot sustain the microorganisms. This may be the case

when the CO concentration and/or hydrogen concertation is

too low. This may be the result of altered reaction circumstances for the Fischer-Tropsch reaction. This may occur during start-up or shut-down of a Fischer-Tropsch reactor.

In an aspect the fermentation product is subjected to

distillation to separate at least the alcohol from the

fermentation product. The raw liquid product exiting the

reactor in which the fermentation is conducted is often

referred to as broth. After the broth is obtained from the

bioreactor part of the biomass is separated from the broth

to obtain an alcohol-rich stream. . The alcohol-rich stream

is fed to a conventional alcohol separation setup

containing two distillation columns and a molecular sieve

unit (MSU) to produce fuel-grade alcohol. Advantageously,

the energy generated by the Fischer-Tropsch reaction may be

used in the distillation process.

The broth (a dilute acetic acid/nutrient solution) is

then cooled to 37 0C before being returned to the reactor.

Optionally nutrients and water are added to the broth

before it is provided to the reactor. The water added to

the broth may be demi water but is preferably process water

obtained from other processes like the water generated by

the Fischer-Tropsch reaction.

Description of the drawings

Figure 1 shows a schematic representation of the

present invention. The system depicted in Figure 1

comprises a bioreactor 1, a scrubber 2 and an alcohol

separation unit 3. Stream 4 represents a carbon monoxide

and hydrogen containing gas mixture. Stream 4 is provided

to the bioreactor 1 in which the carbon monoxide is

converted into alcohol. Stream 4 has a pressure of 10 bar or less and preferably has a temperature of 400C or less and is preferably maintained between 35 and 40°C.

The bioreactor 1 contains microorganisms which

facilitate the conversion process of carbon monoxide to

alcohol. Alcohol is present in two streams leaving

bioreactor 1. Namely, gaseous stream 7 (off gas) and a

liquid stream 5 which is the fermentation broth. The broth

exiting the reactor is filtered to remove microbes (not

depicted). The alcohol-rich stream is fed to a conventional

alcohol separation unit 3 containing two distillation

columns and a molecular sieve unit (MSU) to produce fuel

grade alcohol 6.

The gaseous stream 7 exiting bioreactor 1 is fed to

scrubber 2. Gaseous stream 7 may comprise alcohols, water

and hydrogen and may be scrubbed to remove water and

alcohol. The water and alcohol comprising stream leaving

scrubber 2 may be fed together with or separately of the

broth 5 to alcohol separation unit 3. Gaseous stream 8

leaving scrubber 2 may still contain hydrogen. Hence stream

8 may be provided to a pressure swing adsorption unit (not

depicted) in order to obtain a hydrogen enriched gas

stream.

The broth obtained after treatment in alcohol

separation unit 3 may be provided to the bioreactor 1.

Optionally, nutrients are provided to broth 10 prior to

introduction of the broth to bioreactor 1.

While the invention has been described in terms of what

are presently considered to be the most practical and

preferred embodiments, it is to be understood that the

disclosure need not be limited to the disclosed

embodiments. It is intended to cover various modifications, combinations and similar arrangements included within the spirit and scope of the claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures. The present disclosure includes any and all embodiments of the following claims.

It should also be understood that a variety of

changes may be made without departing from the essence of

the invention. Such changes are also implicitly included in

the description. They still fall within the scope of this

invention.

Any patents, publications, or other references

mentioned in this application for patent are hereby

incorporated by reference. In addition, as to each term

used, it should be understood that unless its utilization

in this application is inconsistent with such

interpretation, common dictionary definitions should be

understood as incorporated for each term and all

definitions, alternative terms, and synonyms such as

contained in at least one of a standard technical

dictionary recognized by artisans. One or more of the

aspects of the invention may be combined and the appended

claims form an integral part of this description by way of

this reference.

Disclosedherein are the followingforms:

1. A process for preparing a paraffin product from a

carbonaceous feedstock comprising the following steps:

(a) Treatment of the carbonaceous feedstock to obtain

a gas mixture comprising hydrogen and carbon monoxide;

(b) Performing at least once, a Fischer-Tropsch reaction

using the gas mixture as obtained in step (a) and

recovering a paraffin product and an off-gas comprising

hydrocarbons, carbon dioxide, carbon monoxide, water and

hydrogen and optionally, nitrogen, argon and traces of

olefins and oxygenates, from the Fischer-Tropsch reaction;

and

(c) Subjecting at least a part of the off-gas from the

Fischer-Tropsch reaction, optionally after removing

hydrocarbons, to anaerobic fermentation to obtain a

fermentation product comprising alcohol.

2. A process according to form 1 wherein the

Fischer-Tropsch reaction is conducted at elevated pressure

and theprocess comprises a further step prior to step (c)

whereinthe off gas pressure is lowered to a pressure of

less than10 bar, prior to subjecting said off gas to

fermentation.

3. A process according to any one of the preceding forms

wherein a part of the gas mixture obtained in step (a) is

subjected to anaerobic fermentation to obtain afermentation

product comprising alcohol.

4. A process according to any one of the preceding forms

wherein the fermentation is affected by at least one member of the carboxydotrophic bacteria such as Clostridium autoethanogenum.

5. A process according to any one of the preceding forms

wherein hydrogen is removed from the off gas prior to

fermentation by means of pressure swing adsorption or after

fermentation from a second off gas obtained in step (c).

6. A process according to any one of the preceding forms

wherein the fermentation product is subjected to

distillation to separate at least the alcohol from the

fermentation product.

7. A process according to any one of the preceding forms

wherein step (c) is performed in two or more bioreactors.

8. A process according to anyone of the preceding forms

wherein in step (a) the gas mixture is obtained by steam

reforming and/or from the partial oxidation of natural gas.

9. A process according to any one of forms 1-8 wherein in

step (a)the gas mixture is obtained by partial combustionof

coal.

Claims (11)

1. A process for preparing a paraffin product from a carbonaceous feedstock comprising the following steps: (a) Treatment of the carbonaceous feedstock to obtain a gas mixture comprising hydrogen and carbon monoxide; (b) Performing at least once, a Fischer-Tropsch reaction at a pressure in the range of from 20 to 80 bar, using the gas mixture as obtained in step (a) and recovering a paraffin product and an off-gas comprising hydrocarbons, carbon dioxide, carbon monoxide, water and hydrogen, from the Fischer-Tropsch reaction wherein the off gas has a CO level of at least 20 vol% ; and (c) Subjecting at least a part of the off-gas from the Fischer-Tropsch reaction to anaerobic fermentation such that at least 50% of the carbon monoxide is converted into alcohol and to obtain a fermentation product comprising alcohol;

wherein the process comprises a step prior to step (c) wherein the off gas pressure is lowered to a pressure in the range of 5 to 10 bar.

2. The process of claim 1, wherein the off-gas comprises nitrogen, argon and traces of olefins and oxygenates.

3. The process of claim 1 or 2, wherein prior to step (c), hydrocarbons are removed from the at least part of the off-gas from the Fischer-Tropsch reaction.

4. The process according to any one of the preceding claims, wherein the fermentation is affected by at least one member of the carboxydotrophic bacteria.

5. The process according to claim 4, wherein the at least one member of the carboxydotrophic bacteria comprises Clostridium autoethanogenum.

6. The process according to any one of the preceding claims, wherein hydrogen is removed from the off-gas prior to fermentation by means of pressure swing adsorption or after fermentation from a second off-gas obtained in step (c).

7. The process according to any one of the preceding claims, wherein the fermentation product is subjected to distillation to separate at least the alcohol from the fermentation product.

8. The process according to any one of the preceding claims, wherein step (c) is performed in two or more bioreactors.

9. The process according to any one of the preceding claims, wherein in step (a) the gas mixture is obtained by steam reforming and/or from the partial oxidation of natural gas.

10. The process according to any one of claims 1-8, wherein in step (a) the gas mixture is obtained by partial combustion of coal.

11. A paraffin product produced according to the process of any one of claims I to 10.

Shell Internationale Research Maatschappij B.V. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON